1. Field of the Invention
This invention relates generally to filtration equipment capable of high density filling of the fillers for liquid chromatography, and more particularly high density filler type filtration equipment for analyzing specific materials in the liquid, or the separating and recovering thereof.
2. Description of the Related Art
A column for liquid chromatography as generally known in filtration equipment has a comparatively small scale of quantity. The equipment will be described by referring to a conventional liquid chromatograph. The equipment is used for separating or isolating specific materials in the liquid by the difference of permeating speeds when the liquid is passed through the fluid paths installed on the cover of a cylindrical casing, wherein fillers are filled in the column and both ends of the column are sealed.
As for the fillers used for the column, it is common to use inorganic powders (such as silica), resin powders (such as polystyrene resin, acrylate resin) usually in fine grains with diameters of under several hundred .mu.m, or organic resin powders (such as polystyrene resin, acrylate resin) in slurry conditions to fill in the column.
Furthermore, it is functionally necessary for the column to pass the process liquid but to prevent the fillers within the column from flowing out. Water permeable filter cloths or multi-hole filter plates are installed inside of both ends of the cover of the column as partition membranes. Generally, synthetic resin membranes and filter cloths are used as partition membranes when applying low pressure for the liquid to pass, and solid partition membranes of the multi-hole plate type, such as stainless steel sintered plates, are used when applying high pressure.
Recently, demand has been increasing for the refinement and recovery of the prescribed materials by using the aforementioned column on an industrial scale. In this case, merely expanding the scale of equipment used in the testing room or laboratory will cause various problems to arise from the points of view of workability, especially in safety, and operation for assembling the equipment or replacing parts.
For example, large sized equipment requires large diameter covers to be inserted on open ends of the cylindrical casing of the column. Accordingly, the weight of the covers increases and in some cases it amounts to several tens of kilograms to several hundereds of kilograms. Therefore, machines such as hoists are required to set the cover. In that case, simplification of the work of using such a machine for setting is strongly needed and the structure of the column should be designed in conformity with this need.
For example, FIG. 5(a) and FIG. 5(b) show examples of a structure of the equipment used in the test room and the laboratory. Concerning the cover 22 which is attached to the column body 21, FIG. 5(a) is an example of the structure to which a cloth partition membrane 25 is pre-installed and FIG. 5(b) is an example of the structure to which a solid partition membrane formed of the multi-hole plate 27 is pre-installed.
In FIG. 5(a), when a filter cloth 25 or the like is installed to the cover 22, a shaping ring 25a as an auxiliary elastic member for press-fitting is suitably fixed in the inner circumferential groove of the cover 22. Even in that case, high tension of the filter cloth is required to keep the cloth from falling due to dead weight. Thus, shortcomings such as deformations of the shape and size of the filter cloth apertures are observed.
In FIG. 5(b), on the other hand, a seal ring 26 such as PTFE (polytetrafluoroethylene and the like) is used for installing the multi-hole plate 27 as a solid partition membrane in the cover 22. The coefficient of friction is small in PTFE and so extremely high precision in dimensional accuracy is required for the solid partition membrane 27 of the multi-hole plate having a large diameter of more than 200 mm to be frictionally gripped. Besides, temperature change is taken into consideration for elasticity and so the exact installation is difficult. Moreover, when ease of replacing the parts is taken into consideration, such structures as mentioned above are impractical for use. Furthermore, various methods such as calking, fitting with screws or fitting with pins may be applied for fixing the aforementioned partition membrane to the cover. But these methods may make it impossible to replace the partition plate upon the occurrence of partial standing fluids and corrosion. Accordingly, these methods are not suitable for a fluid process type column.
From the viewpoints mentioned above, the present inventors developed filtration equipment in which the partition membrane and the seal ring are installed in the cover beforehand for the purpose of simplicity when the equipment is assembled. FIG. 6 shows a column provided with such a structure. The equipment shown in FIG. 6 is not admitted to be prior art and has the following structure: An outer circumferential flange 1a of column body 1 is used for detachably connecting a cover 2 around the upper end of the column body. The cylindrical column body 1 is filled with filler. The cover 2 has a fluid path 2a and is lockably attached to the upper open end of the column body 1 to seal the upper open end when the aforementioned fillers are filled. A seal ring 6 is prearranged on a flange which extends downward from the circumference of the cover 2, is inserted in a groove on the outer circumferential flange of the column body 1 and seals the flange when lockable attachment is made by bolts 3 passing through holes 1b and 2b. The structure of the plate 7 and ring 6 is preattached to the cover and prevents the filler within the column body from flowing out when the cover is press-fitted on the column body.
The objective of improving the assembling of a column for liquid chromatography is attainable by the structure mentioned above, however since the column is used for separating the prescribed materials, a predetermined separation capability ought to be maintained. High density filling of the filler is required for the purpose.
When the filler is filled into the column for liquid chromatography, a common technique is that filler powders are mixed with liquid to make slurry, which is poured into the column, and the liquid is extracted to attain high density, uniform filling of the filler within the column. Such a filling operation cannot be easily realized even with the improved filtration equipment of FIG. 6. This is due to the fact that the slurry overflows from the upper end of the column body when the cover is attached to the column body.